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# C Sample Question

1. ```main( )
{
int a[2][3][2] = {{{2,4},{7,8},{3,4}},{{2,2},{2,3},{3,4}}};
printf("%u %u %u %d \n",a,*a,**a,***a);
printf("%u %u %u %d \n",a+1,*a+1,**a+1,***a+1);
}```

100, 100, 100, 2
114, 104, 102, 3

Explanation:

The given array is a 3-D one. It can also be viewed as a 1-D array.
 2 4 7 8 3 4 2 2 2 3 3 4
 100 102 104 106 108 110 112 114 116 118 120 122

thus, for the first printf statement a, *a, **a give address of first element . since the indirection ***a gives the value. Hence, the first line of the output.

for the second printf a+1 increases in the third dimension thus points to value at 114, *a+1 increments in second dimension thus points to 104, **a +1 increments the first dimension thus points to 102 and ***a+1 first gets the value at first location and then increments it by 1. Hence, the output.

2. ```main( )
{
int a[ ] = {10,20,30,40,50},j,*p;
for(j=0; j<5; j++)
{
printf("%d" ,*a);
a++;
}
p = a;
for(j=0; j<5; j++)
{
printf("%d " ,*p);
p++;
}
}```

Compiler error: lvalue required.

Explanation:

Error is in line with statement a++. The operand must be an lvalue and may be of any of scalar type for the any operator, array name only when subscripted is an lvalue. Simply array name is a non-modifiable lvalue.
3. ```main( )
{
static int  a[ ]   = {0,1,2,3,4};
int  *p[ ] = {a,a+1,a+2,a+3,a+4};
int  **ptr =  p;
ptr++;
printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr);
*ptr++;
printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr);
*++ptr;
printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr);
++*ptr;
printf("\n %d  %d  %d", ptr-p, *ptr-a, **ptr);
}```

111
222
333
344

Explanation:

Let us consider the array and the two pointers with some address

a
 0 1 2 3 4
 100 102 104 106 108

p
 100 102 104 106 108
 1000 1002 1004 1006 1008

ptr
 1000
 2000

After execution of the instruction ptr++ value in ptr becomes 1002, if scaling factor for integer is 2 bytes. Now ptr - p is value in ptr - starting location of array p, (1002 - 1000) / (scaling factor) = 1, *ptr - a = value at address pointed by ptr - starting value of array a, 1002 has a value 102 so the value is (102 - 100)/(scaling factor) = 1, **ptr is the value stored in the location pointed by the pointer of ptr = value pointed by value pointed by 1002 = value pointed by 102 = 1. Hence the output of the firs printf is 1, 1, 1.

After execution of *ptr++ increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the second printf are ptr - p = 2, *ptr - a = 2, **ptr = 2.

After execution of *++ptr increments value of the value in ptr by scaling factor, so it becomes1004. Hence, the outputs for the third printf are ptr - p = 3, *ptr - a = 3, **ptr = 3.

After execution of ++*ptr value in ptr remains the same, the value pointed by the value is incremented by the scaling factor. So the value in array p at location 1006 changes from 106 10 108,. Hence, the outputs for the fourth printf are ptr - p = 1006 - 1000 = 3, *ptr - a = 108 - 100 = 4, **ptr = 4.

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